Wireless communication has become more and more popular in recent years because a wireless device has the advantages of portability. A user can obtain information or communicate with others anywhere using a wireless device without being confined to his (or her) location. In general, a wireless device needs to have a transmitting part, a receiving part and an antenna for wireless communication.
In a conventional wireless device, the antenna is mainly a dipole which is formed by a metal rod or a helical cylinder, and is usually extended out from the wireless device. In order for a wireless device to be easily portable, a new trend in manufacturing the device is to make it as compact as possible. Thus, in recent years the design of antennas has been improved greatly. The first improvement is minimizing the size of the antenna. Nevertheless, the conventional antenna has several drawbacks. The antenna itself has significantly enlarged the size of the wireless device. The antenna is extended out from the device, and thus easy to pierce the body of its user. Furthermore, it is easily broken.
To overcome these drawbacks, a foldable antenna has been invented. In general, the foldable antenna can be hidden within the housing of a wireless device. If it is used, the user draws the antenna from the housing. Although a foldable antenna has solved some of the problems, it is still inconvenient to the user.
Recently, a novel antenna design has been disclosed. The concept of patch antennas is employed in the new design. This type of antenna is called "printed circuit antenna". Printed circuit antennas have been utilized in the field of radio communications to provide a light weight antenna. U.S. Pat. No. 5,495,260 to Couture is an example of a simple dipole antenna implemented in the form of a printed circuit antenna. U.S. Pat. No. 4,758,843 to Agrawal shows a planar printed circuit substrate having a plurality of dipole antennas and a feed network including a sum and difference hybrid printed circuit thereon. U.S. Pat. No. 5,206,657 to Downey shows a printed circuit radio frequency antenna comprising a pair of double-sided printed circuit boards spaced apart by standoffs.
An antenna with high directivity has always been desired for its efficiency in direct point-to-point radio communication. It is very useful in radio communication to have a printed circuit antenna with high directivity. In addition to its light weight, a planar printed circuit antenna has the advantage that it can be formed at the same time and on the same substrate with other circuit sections. The wireless transceiver system can use this feature to make an integrated system on a printed circuit board to reduce the manufacturing time and cost. The absence of mechanical structures or connectors in the antenna construction also improves the reliability of the wireless transceiver system.
Unfortunately, the existing printed circuit antennas in various configurations do not provide a simple solution for the high directivity antenna. There is a need to develop a printed circuit antenna which has a planar structure to be integrated with other electronic circuits, exhibits higher directivity than a single dipole antenna, and occupies a relatively smaller area on a substrate.